A very good suggestion, Sander.
A blinking function is indeed very necessary for previews. Actually, I have it in mind since some time ago, and even I considered including it in the current 1.2 version. But I want to add more functionality to previews, and decided to postpone this one until I have a more complete set of changes ready to be implemented.
Anyway, it's true that this feature is very easy to write, so count with it for the next version (which, considering the amount and nature of the bugs being discovered recently, should happen quite soon). I'll include also an equivalent feature in the real-time preview window.
Thank you for your nice words about PixInsight's previews. Previews are an important and very characteristic part of our interface paradigm, so I'm very happy to know that you like them. I look forward to know any ideas you may have to improve their functionality.